1. Field of the Invention
The present invention relates generally to a an electroacoustic transducer unit for use in communication terminals.
2. Background of the Related Art
In communication terminals, such as telephone stations, three electro-acoustic transducers are necessary, namely a microphone, a receiver, and a signaling device such as a voice frequency ringing transducer. Using the piezo-electric principle, all of these transducers operate according to the same scheme. In the case of microphone, the transducer plate is provided with a piezo-electric layer and an unpitched sound is directed against the transducer plate, which converts the sound into an alternating current. In the case of a receiver and a voice frequency ringing transducer, it is vice versa. In other words, an alternating electric signal is directed to the piezoelectric layer so that a sound is produced. However, voice frequency ringing differs from the operating of a receiver basically in that it radiates certain frequencies at a particularly loud amplitude. Thus, the natural resonance of the transducer diaphragm and the resonance of the acoustic spaces is preferably utilized rather than controlled. In the case of a receiver and a microphone, however, the resonance of the membrane is dampened to gain a uniform frequency response.
To lower the costs for storing and manufacturing, it is desirable to use the same type of electro-acoustic transducer for a microphone, a receiver, and a voice frequency ringing transducer.